Defects in bone structure arise in a variety of circumstances, such as trauma, disease, and surgery. There is a need for effective repair of bone defects in various surgical fields, including maxillo-craniofacial, periodontics, and orthopedics. Numerous natural and synthetic materials and compositions have been used to stimulate healing at the site of a bone defect. As with compositions used to repair other types of tissue, the biological and mechanical properties of a bone repair material are critical in determining the effectiveness and suitability of the material in any particular application.
After blood, bone is the second most commonly transplanted material. Autologous cancellous bone has long been considered the most effective bone repair material, since it is both osteoinductive and non-immunogenic. However, the use of autologous cancellous bone is not available under all circumstances, and donor site morbidity and trauma are serious drawbacks to this approach. The use of allograft bone avoids the problem of creating a second surgical site in the patient, but suffers from some disadvantages of its own. For instance, allograft bone typically has a lower osteogenic capacity than autograft bone, a higher resorption rate, creates less revascularization at the site of the bone defect, and typically results in a greater immunogenic response. The transfer of certain diseases is also a danger when using allografts.
To avoid the problems associated with autograft and allograft bone, considerable research has been conducted in the area of synthetic bone substitute materials that can be used in lieu of natural bone material. For example, various compositions and materials comprising demineralized bone matrix, calcium phosphate, and calcium sulfate have been proposed. In many instances, however, the synthetic bone materials proposed in the art have suffered from significant disadvantages. For example, some compositions fail to provide the structural support necessary to augment the healing process. Other compositions fail to adequately mimic the density and overall physical structure of natural bone, which can lead to reduced performance. This can be particularly problematic when replacing cancellous (trabecular) bone material, which has a distinct reticulated pore structure that can be difficult to mimic in a synthetic construct. Further, some materials suffer from a reabsorption rate that improperly paces the natural healing process and, thus, fail to provide the necessary framework for the ingrowth of new tissue.
There remains a need in the art for improved bone substitute materials suitable for use in bone graft compositions, particularly materials that can be used as a replacement for cancellous bone.